1. Field of the Invention
The present invention relates to an organic electroluminescence device, and more particularly to an organic electroluminescence device with an improved heat radiation structure.
2. Description of the Related Art
Electroluminescence devices are classified into an inorganic electroluminescence device and an organic electroluminescence. The organic electroluminescence is more advantageous than the inorganic electroluminescence device in view of a low voltage driving, a high brightness, and three primary color luminescence. The organic electroluminescence has been on the aggressive developments for application to a flat panel display and a surface light source.
FIG. 1 is a fragmentary cross sectional elevation view of a conventional electroluminescence device. The conventional electroluminescence device has the following structure. An anode layer 6 overlies a glass substrate 20. A hole transport layer 7 overlies the anode layer 6. A luminescence layer 8 overlies the hole transport layer 7. An electron transport layer 9 overlies the luminescence layer 8. A cathode layer 10 overlies the electron transport layer 9.
Organic materials are available for the hole transport layer 7, the luminescence layer 8 and the electron transport layer 9. Holes are injected from the anode layer 6 into the luminescence layer 8. Electrons are injected from the cathode layer 10 into the luminescence layer 8. The injected holes and electrons are re-combined in the luminescence layer 8 for causing a luminescence.
Some of the organic materials, which are available for the hole transport layer 7, the luminescence layer 8 and the electron transport layer 9, show cohesion and crystallization at a low temperature of about 100xc2x0 C. When the organic electroluminescence device is driven at a current density of about a few hundreds mA/cm2, a local heat generation is caused for deteriorating characteristics or performances of the organic electroluminescence device.
To have solved the above problems, the following conventional proposals have been made. Japanese laid-open patent publication No. 5-129082 discloses that a metal oxide with a high heat conductivity is added to a glass substrate, so that the glass substrate has an improved heat conductivity. Japanese laid-open patent publication No. 10-144468 discloses that a sapphire substrate or a quartz substrate is used due to those high heat conductivity. Japanese laid-open patent publications Nos. 7-111192 and 10-275681 disclose that a heat radiation layer is provided over a cathode for improving the device in heat radiation characteristic.
Japanese laid-open patent publications Nos. 10-144469, 10-214683, and 2000-48951 disclose that the organic electroluminescence device is provided over a plastic substrate. The plastic substrate is superior than the glass substrate in shock resistivity, light weight and reduced thickness. Thus, the plastic substrate is more suitable than the glass substrate as a mounting substrate for the organic electroluminescence device for application to mobile terminal displays and flexible displays. For those reasons, the plastic substrate is attractive.
The plastic substrate is, however, smaller in heat conductivity than the glass substrate, for which reason the organic electroluminescence device with the plastic substrate is inferior in heat radiation characteristic than the organic electroluminescence device with the glass substrate. As compared to the organic electroluminescence device with the glass substrate, the organic electroluminescence device with the plastic substrate is likely to be deteriorated in characteristic at a relatively low driving current density.
Thus, the organic electroluminescence device with the plastic substrate is lower than the organic electroluminescence device with the glass substrate in the upper limit driving current density for avoiding the deterioration in characteristic. A brightness of the organic electroluminescence device depends on the driving current density. The maximum brightness of the organic electroluminescence device is limited by the upper limit driving current density for avoiding the deterioration in characteristic. Thus, the organic electroluminescence device with the plastic substrate is lower in the maximum brightness than the organic electroluminescence device with the glass substrate. Further, the organic electroluminescence device with the plastic substrate is shorter in life-time under continuous driving condition than the organic electroluminescence device with the glass substrate.
The heat radiation layer over the cathode of the organic electroluminescence device provides a beat radiation effect which is, however, insufficient for solving the above problems with the use of the plastic substrate.
In the above circumstances, the development of a novel organic electroluminescence device with a plastic substrate and an improved heat radiation structure, which is free from the above problems, is desirable.
Accordingly, it is an object of the present invention to provide a novel organic electroluminescence device with a plastic substrate and an improved heat radiation structure, which is free from the above problems.
It is a further object of the present invention to provide a novel organic electroluminescence device with a plastic substrate and an improved heat radiation structure which suppresses an excess local temperature increase.
It is a still further object of the present invention to provide a novel organic electroluminescence device with a plastic substrate and an improved heat radiation structure for allowing a high maximum brightness.
It is yet a further object of the present invention to provide a novel organic electroluminescence device with a plastic substrate and an improved heat radiation structure allowing a long life-time under continuous driving conditions.
It is further more object of the present invention to provide a novel organic electroluminescence device with an improved heat radiation structure and a plastic substrate, wherein the organic electroluminescence device is superior in shock resistivity.
It is moreover object of the present invention to provide a novel organic electroluminescence device with an improved heat radiation structure and a plastic substrate, wherein the organic electroluminescence device is superior in light weight.
It is still more object of the present invention to provide a novel organic electroluminescence device with an improved heat radiation structure and a plastic substrate, wherein the organic electroluminescence device is superior in reduced thickness.
It is yet more object of the present invention to provide a novel organic electroluminescence device with an improved heat radiation structure and a plastic substrate, wherein the organic electroluminescence device is suitable for mobile terminal displays and flexible displays.
It is an additional object of the present invention to provide a novel heat radiation structure of an organic electroluminescence device with a plastic substrate free from the above problems.
It is a further additional object of the present invention to provide a novel heat radiation structure, of an organic electroluminescence device with a plastic substrate, wherein the heat radiation structure suppresses an excess local temperature increase.
It is further more additional object of the present invention to provide a novel heat radiation structure of an organic electroluminescence device with a plastic substrate, wherein the heat radiation structure allows a high maximum brightness.
It is moreover additional of the present invention to provide a novel heat radiation structure of an organic electroluminescence device with a plastic substrate, wherein the heat radiation structure allows a long life-time under continuous driving conditions.
The present invention provides an organic electroluminescence device including a base structure and at least an organic electroluminescence device structure over the base structure, wherein the base structure includes a substrate made of a plastic material, and at least a heat radiation layer which is higher in heat conductivity than the substrate.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.